1. Field of the Invention
The present invention relates to a process and apparatus for extruding mixtures of thermoplastic and thermoset polymers and to articles made therefrom. In another aspect, the present invention relates to a process and apparatus for cooling extruded mixtures of thermoplastic and thermoset polymers and to articles made therefrom, wherein at least one of the polymers is recycled. In even another aspect, the present invention relates to a process and apparatus for cooling extruded mixtures of polyolefins and recycled rubber and to articles made therefrom. In still another aspect, the present invention relates to a process and apparatus for cooling extruded mixtures of polyethylene and tire particles and to articles made therefrom. In yet another aspect, the present invention relates to a process and apparatus for cooling extruded mixtures of polyethylene and tire particles and to articles made therefrom, by forcing air against the top, bottom and side surfaces of the extrudate. In even another aspect, the present invention relates to a process and apparatus for extruding mixtures of thermoplastic and thermoset polymers and to articles made therefrom, utilizing carbon black as a processing aid.
2. Description of the Related Art
Plastic materials are finding utility in more and more applications everyday. For example, plastics are used in all sorts of disposable applications such as diapers, product packaging, utensils, plates, cups, syringes, drink containers and shrink wrap. As another example, plastics are used as a major material of construction for electronic products such as telephones, computers, radios, stereos, kitchen appliances. As further example, plastics are utilized in automobiles in such applications as body molding, bumper guards, hoses, light covers, interior paneling, mud guards, floor mats and tires. In the construction industry, plastics are utilized in electrical wire, telephone wire, as paneling, horizontal surface tops, switches and moldings. Other examples, include the use of plastics in articles of clothing.
Unfortunately, as plastic materials proliferate into every facet of life, such materials become a larger portion of the waste stream. Disposable plastic items are used then disposed. Goods comprising plastic are trashed once the end of the useful life of the good is reached. Plastic waste is even generated during the process of making plastic articles in the form of off-spec material or "flash". Off-spec material may be rejected because of appearance or physical property deficiency. "Flash" refers to excess polymer on a formed article that must be removed from the formed article. The environmental pressures of today stress the recycling of these waste plastic materials whenever possible.
Plastics fall into one of two categories, thermoplastics and thermosets.
Thermoplastics are polymers that will have a softening temperature and a melting temperature. Examples of thermoplastics include polyvinyl chloride, nylon, polyurethane and polyolefins, Heating a thermoplastic above its softening temperature will soften it, and heating it above its melting temperature will melt it. It is easy to see that thermoplastics can be formed into a shape, melted and reformed. Thus thermoplastics lend themselves to recycling.
Thermosets, on the other hand, do not readily lend themselves to recycling. A thermoset is a polymer that solidifies or "sets irreversibly. Examples of thermosets include, phenolics, polyesters, rubber and synthetic rubber. Since these polymers irreversibly set, heating them does not melt them into a reformable liquid. Thermosets are thus difficult to recycle.
As old vehicle tires are generally considered to constitute an environmental eyesore, many efforts have been made to recycle tires.
U.S. Pat. No. 3,210,301, issued Oct. 5, 1955, to White discloses a rubber compounding product that is made by recycling vulcanized reclaimed rubber from tires by first removing fibers and then mechanically working the rubber in the presence of 0.1-35 parts atactic polypropylene per hundred parts rubber.
Several patents disclose the use of rubber in making a molding composition. For example, U.S. Pat. No. 3,267,187, issued Aug. 5, 1955 to Siosberg et al., discloses that rubber granules may be mixed with a thermoplastic resin and molded into sheets. Also, U.S. Pat. No. 4,320,082, issued Mar. 15, 1982 to Houle, discloses a molding composition made from rubber, nylon and a vulcanizing agent, such as sulfur or magnesium oxide. U.S. Pat. No. 4,481,335, issued Nov. 6, 1984, discloses a rubber molding composition comprising tire rubber scrap, a sulfur curable polymeric binder and a curing agent for the binder. Finally, U.S. Pat. No. 4,795,603, issued Jan. 3, 1989 to Nagayasu, discloses an injection molding composition comprising 10-20 percent rubber particles and 70-90 percent polyethylene or Polypropylene waste. However, these compositions are generally for batch type molding processes rather than a Continuous extrusion type process.
U.S. Pat. No. 4,028,288, issued Jun. 7, 1977, and U.S Pat. No. 4,003,408, issued Jan. 18, 1977, both to Turner, both disclose processes for reclaiming tire rubber utilizing particalized tires, but excluding the metallic content thereof. Turner '288 limits the amount of cord content to less than 10 percent. Thus neither Turner patent discloses a method for processing the whole tire.
Finally, U.S. Pat. No. 4,970,043, issued Nov. 13, 1990, discloses a method of recycling "high grade" rubber having reduced debris as compared to reground rubber obtained from many automobile tires. The high grade rubber is extruded with a thermoplastic to form a semi-stable moldable product which is then cooled to form a stable moldable product. Since this process requires "high grade" rubber, tires containing debris cannot be processed.
Applicant is the coinventor of grandparent application, now U.S. Pat. No. 5,312,573, which discloses an apparatus and process which reuse whole tire waste, including metal and fabric belts and tire beads. As disclosed in the '573 patent, the extrudate is dimensionally stable as it leaves the cooling chamber 58 of the extruder. As the extrudate travels along conveyor 96, it is subjected to cooling as it passes through ambient air.
Numerous attempts have been made to address the cooling of an extrudate as it leaves an extrusion die or cooling chamber.
Principles Of Polymer Systems, Ferdinand Rodriguez, McGraw-Hill, 1972, at 322-327, discloses that air-cooling may be utilized to cool an extrudate in order to gain dimensional stability.
U.S. Pat. No. 3,242,529, issued Mar. 29, 1966 to Parr et al., discloses a melt spinning apparatus with oppositely directed inert gas streams for continuously supplying an inert gas at the temperature of the spinnerette to the vicinity of the face of the spinnerette plate to prevent the occurance of "drip". The inert gas is provided under conditions that will not substantially alter the normal extrusion and cooling conditions.
U.S. Pat. No. 3,460,200, issued Aug. 12, 1969 to Zaitsev et al., discloses a cabinet for air-stream cooling of filament spun from a polymeric melt, in which a plurality of partitions form sections to provide guided travel of the air stream across the filaments to preclude whirls in the steam as well as its endwise motion along the filament bundle.
U.S. Pat. No. 3,502,763, issued Mar. 24, 1970 to Hartmann, discloses a process of producing non-wovon fabric fleece in which fused polymer is extruded from spinneret holes in filament form, and immediately thereafter seized on both sides by heated gas currents dischared from two slit-like openings in the direction of travel of the filaments.
U.S. Pat. No. 4,133,620, issued Jan. 9, 1979 to Lehner, discloses a polymer filament manufacturing device in which a cooling gas is passed across extruded filaments through a multiplicity of nozzles arranged on one side of the filaments.
U.S. Pat. No. 4,452,752, issued Jun. 5, 1984 to Harder et al., discloses a method and apparatus for extruding a thermoplastic shape along a shaped cooling surface.
U.S. Pat. No. 4,801,458, issued Mar. 7, 1989 to Oshima et al., discloses a process for extrusion-molding cermic bodies, which includes continuously extruding a ceramic body through a die of an extruder and holding it on a porous support at a slightly floating shape by an air pressure which is jetted from pores of the support onto the underside of the ceramic body.
U.S. Pat. No. 5,108,277, issued Apr. 28, 1992 to Dixon, discloses an apparatus for cooling extruded material, which apparatus supports the extrudate on a cushion of air while controlling the temperature of the air.
U.S. Pat. No. 5,141,700, issued Aug. 25, 1992 to Sze, discloses a melt spinning process for polyamide industrial filaments, in which the freshly-extruded filaments enter an enclosed zone that is maintained at superatmospheric pressure by a controlled flow of air at low positive pressure and the filaments leave the zone through a constriction, either a venturi or a tube, assisted by the concurrent flow of such air at a high controlled velocity.
In spite of the above methods, there is a need for an improved method and apparatus of cooling an extrudate as it leaves an extrusion die or cooling chamber.
This and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.